1. Field of the Invention
The present invention relates to a sample inspecting apparatus for inspecting a sample typified by a semiconductor wafer. More specifically, the present invention relates to a macro inspection mechanism of the sample inspecting apparatus which is suitable for a visual inspection of a sample, in particular both back and front surfaces of the sample.
2. Description of Related Art
A semiconductor wafer having a predetermined pattern formed thereon goes through inspections which are roughly divided into two. One is a macro inspection which is a visual inspection by an inspector for presence or absence of scratches or dust. The other is a micro inspection which is an inspection, with a microscope, of a state of the pattern formed on the surface.
Generally in the macro inspection of a semiconductor wafer, a wafer is illuminated by illumination light thereby to visually inspect the reflected light therefrom for inconsistencies in color, scratches, dust and the like. Upon this type of inspection, conventionally, a semiconductor wafer is adsorbed and held by a macro stage, and then the macro stage is rotated or inclined so as to change the state of the wafer surface for the visual inspection. In recent years, it has been more and more general to enlarge a wafer diameter and to fine its pattern. As a result, small dust which has been overlooked without any problems in the past may cause deficiency, and therefore problems associated with dust are getting more difficult.
Also, flatness of a back surface of the wafer has come to greatly influence the state of pattern, so that more importance has been attached to the necessity for inspecting the back surface of the wafer. One suggested apparatus for this type of inspection is provided with a wafer holding part, apart from a front surface inspection mechanism, which adsorbs or holds the wafer by the periphery to lift the wafer to a position where the inspector can observe the back surface of the wafer (see FIG. 6). This type of inspecting apparatus operates to place the wafer on a macro stage once to perform the front surface inspection, and then to release the adsorption by the macro stage. Thereafter the wafer holding part lifts the wafer.
However, the conventional macro inspecting apparatus has the following problems.
(a) In the mechanism which adsorbs and holds the back surface of the wafer, the wafer has contact with the adsorptive surface. This results in a possibility of adhesion of dust.
(b) The mechanism which lifts the wafer with the wafer holding part by adsorbing and holding upon the back surface inspection also has a possibility that dust may adhere to the back surface of the wafer. In addition, portion of the wafer where the wafer holding part adsorbs the wafer is obstructed. In short, the disadvantage is that there is an uninspected portion is left and the portion can not be inspected.
(c) The mechanism which lifts the wafer with the wafer holding part to perform the back surface inspection disadvantageously provides an inspector different points of view between the front surface inspection and the back surface inspection. For this reason, stable and accurate inspections can not be performed.
(d) In the front surface inspection, it is possible to rotate or incline the wafer with the macro stage to allow inspection from various angles. In the back surface inspection, however, the wafer is held still with the wafer holding part during the inspection. Therefore, the inspection is performed only at one specific angle to be insufficient.
(e) In a macro inspection, the wafer is illuminated and the inspection is performed using the reflected light therefrom. To deal with the different positions of the wafer upon the front surface inspection and the back surface inspection, illumination units need to be provided at suitable positions for each inspection.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a sample inspecting apparatus which is capable of reducing adhesion of dust to the back surface of the wafer and of stably performing the front surface inspection as well as the back surface inspection under the even conditions.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, a sample inspecting apparatus of this invention which performs a visual inspection of a sample to be inspected by reflected light therefrom, the apparatus comprises holding means which holds the sample at its periphery, first rotating means which rotates the holding means on a first axis passing through an approximate center of the sample being held by the holding means and second rotating means which rotates the holding means on a second axis passing through the approximate center of the sample being held by the holding means.
In another aspect of the present invention, a sample inspecting apparatus of this invention which performs a visual inspection of a sample to be inspected by reflected light therefrom, the apparatus comprises a holder which holds the sample at its periphery, first rotation mechanism which rotates the holder on a first axis passing through an approximate center of the sample being held by the holder and second rotation mechanism which rotates the holder on a second axis passing through the approximate center of the sample being held by the holder.
As described, according to the present invention, a sample such as a wafer can be placed in the same position under the same condition in the front surface inspection and the back surface inspection. This eliminates the necessity that the inspector changes his point of view for each inspection.
In addition, it also eliminates the necessity to provide different illumination units for the front surface inspection and the back surface inspection or to move one illumination unit upon each inspection. Therefore, the inspection can be performed efficiently.
Further, since it is unnecessary to switch the hold of the wafer upon inspecting the front surface and the back surface of the sample, the inspection can carry out smoothly.
Still further, the inspection of both surfaces of the sample may be performed without adapting a mechanism to adsorb the sample. Accordingly, the inspection can be performed without leaving an uninspected part upon the back surface inspection and contamination by dust can be reduced as well.